JP5064692B2 - Manufacturing method of SOI substrate - Google Patents

Description

  The present invention relates to a method for manufacturing an SOI substrate having a single crystal silicon thin film on a transparent insulating substrate.

  As a conventional method for manufacturing an SOI substrate by bonding, a SmartCut method, a SiGen method, or the like is known.

  In the SmartCut method, a silicon substrate into which hydrogen ions are implanted on the bonding surface side is bonded to a silicon substrate or another material substrate, and a heat treatment of 400 ° C. or higher (for example, 500 ° C.) is performed. In this method, the silicon thin film is thermally peeled from the highest region to obtain an SOI substrate (for example, Patent Document 1 and Non-Patent Document 1).

In addition, the SiGen method performs plasma treatment on both or one of the bonding surfaces of these substrates before bonding the silicon substrate implanted with hydrogen ions to the bonding surface and the silicon substrate or another material substrate. Then, after bonding the two substrates with their surfaces activated, heat treatment is performed at a low temperature (for example, 100 to 300 ° C.) to increase the bonding strength, and then mechanically peeling at room temperature to obtain an SOI substrate (For example, Patent Documents 2 to 4).
Japanese Patent No. 3048201 US Pat. No. 6,263,941 US Pat. No. 6,513,564 US Pat. No. 6,582,999 AJ Auberton-Herve et al., "SMART CUT TECHNOLOGY: INDUSTRIAL STATUS of SOI WAFER PRODUCTION and NEW MATERIAL DEVELOPMENTS" (Electrochemical Society Proceedings Volume 99-3 (1999) p.93-106).

  The difference between these two methods is mainly in the silicon thin film peeling process. The SmartCut method requires high-temperature treatment for peeling the silicon thin film, but the SiGen method can be peeled off at room temperature.

  In general, in manufacturing a bonded SOI substrate, a silicon substrate and a different type material substrate other than silicon are bonded to each other, but such dissimilar materials usually differ in thermal expansion coefficient, intrinsic heat resistance temperature, and the like. Therefore, if the temperature of the heat treatment applied to the bonded substrate during the manufacturing process increases, cracks and local cracks are likely to occur due to differences in thermal characteristics between the two substrates. From this point of view, the SmartCut method that requires high temperature for peeling the silicon thin film is not preferable as a method for manufacturing an SOI substrate by bonding different types of material substrates.

  On the other hand, the SiGen method, which can be peeled off at a low temperature, is unlikely to cause cracks or local cracks due to differences in thermal characteristics as described above, but in this method of mechanically peeling the silicon thin film, There is a problem that the adhesive surface of the substrate is peeled off, peeling marks are generated, or mechanical damage is easily introduced into the silicon thin film.

  The present invention has been made in view of such problems, and an object of the present invention is to provide thermal processing between substrates in a process of manufacturing an SOI substrate by bonding a single crystal silicon substrate and a transparent insulating substrate. SOI with excellent film thickness uniformity, crystallinity, and various electrical characteristics (carrier mobility, etc.) by avoiding the introduction of cracks, local cracks, etc. due to differences in various characteristics and mechanical damage to the SOI layer. It is to provide an SOI substrate having a layer.

  In order to solve such problems, the present invention provides a method for manufacturing an SOI substrate, wherein a hydrogen ion implanted layer is formed on a surface side of a first substrate which is a single crystal silicon substrate. A second step of performing a surface activation process on at least one of the surface of the second substrate which is a transparent insulating substrate and the surface of the first substrate, and the first substrate. A third step of bonding the surface of the first substrate and the surface of the second substrate, and the back surface of the first substrate of the bonded substrate is brought into close contact with a heating plate maintained at a temperature of 200 ° C. or higher and 350 ° C. or lower. And a fourth step of heating the first substrate and peeling the silicon layer from the first substrate to form an SOI layer on the surface of the second substrate. To do.

  According to a second aspect of the present invention, in the method for manufacturing an SOI substrate according to the first aspect, the second substrate is any one of a quartz substrate, a sapphire (alumina) substrate, a borosilicate glass substrate, and a crystallized glass substrate. It is characterized by.

According to a third aspect of the present invention, in the method for manufacturing an SOI substrate according to the first or second aspect, a hydrogen ion implantation amount (dose amount) in the first step is 1 × 10 ^{16 to} 5 × 10 ^17. It is characterized by atoms / cm ² .

  According to a fourth aspect of the present invention, in the method for manufacturing an SOI substrate according to any one of the first to third aspects, the surface activation treatment of the second step is at least one of plasma treatment or ozone treatment. It is executed.

  According to a fifth aspect of the present invention, in the method for manufacturing an SOI substrate according to any one of the first to fourth aspects, the third step includes the first substrate and the second substrate after the bonding. And a sub-step of heat treatment at 100 to 350 ° C. in a state where the substrates are bonded together.

  According to a sixth aspect of the present invention, in the method for manufacturing an SOI substrate according to any one of the first to fifth aspects, the heating plate used in the fourth step is a semiconductor substrate or a ceramic substrate having a smooth surface. It is characterized by being.

  The invention described in claim 7 is the method for manufacturing an SOI substrate according to any one of claims 1 to 6, wherein the fourth step is performed before or after the heating of the first substrate. A sub-step of applying an external impact for promoting peeling from an end of the ion implantation layer is provided.

  According to the present invention, the back surface of the single crystal Si substrate bonded to the insulating substrate is brought into close contact with a heating plate maintained at a temperature of 200 ° C. or higher and 350 ° C. or lower, and a temperature difference is established between the transparent insulating substrate and the transparent insulating substrate. Since this caused a large stress between the two substrates to peel off the silicon thin film, the silicon substrate suffered from cracks, local cracks, etc. due to differences in thermal characteristics between the substrates and mechanical damage. Introduction into the silicon thin film that is peeled off from the surface region is avoided. As a result, it is possible to provide an SOI substrate having an SOI layer that is excellent in film thickness uniformity, crystallinity, and various electrical characteristics (such as carrier mobility).

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram for explaining a process example of a method for manufacturing an SOI substrate according to the present invention. The first substrate 10 shown in FIG. 1A is a single crystal Si substrate, and the second substrate 20 is quartz. A transparent insulating substrate such as a substrate, a sapphire (alumina) substrate, a borosilicate glass substrate, or a crystallized glass substrate.

  Here, the single crystal Si substrate 10 is a generally commercially available Si substrate grown by, for example, the CZ method (Czochralski method), and has electrical characteristics such as conductivity type and specific resistivity, crystal orientation, and crystal diameter. Is appropriately selected depending on the design value and process of the device provided with the SOI substrate manufactured by the method of the present invention or the display area of the manufactured device.

  Note that these substrates have the same diameter, and for the convenience of the subsequent device formation process, the transparent insulating substrate 20 is also provided with the same OF as the orientation flat (OF) provided on the single crystal Si substrate 10. It is convenient to provide these and match these OFs together.

  First, hydrogen ions are implanted into the surface of the first substrate (single crystal Si group) 10 to form a hydrogen ion implanted layer (FIG. 1B). This ion-implanted surface becomes a later “bonding surface (bonding surface)”. By this hydrogen ion implantation, a uniform ion implantation layer 11 is formed at a predetermined depth (average ion implantation depth L) in the vicinity of the surface of the single crystal Si substrate 10, and the average ions in the surface region of the single crystal Si substrate 10 are formed. In the region corresponding to the implantation depth L, a “microbubble layer” localized in the region is formed (FIG. 1C).

The depth of the ion implantation layer 11 from the surface of the single crystal Si substrate 10 (average ion implantation depth L) is controlled by the acceleration voltage at the time of ion implantation, and depends on how thick the SOI layer is peeled off. It is determined. For example, the average ion implantation depth L is 0.5 μm or less, and the ion implantation conditions are a dose of 1 × 10 ^{16 to} 5 × 10 ¹⁷ atoms / cm ² and an acceleration voltage of 50 to 100 keV.

  In addition, an insulating film such as an oxide film is formed in advance on the ion implantation surface of the single-crystal Si substrate 10 as is normally performed to suppress channeling of implanted ions in the ion implantation process into the Si crystal, Ion implantation may be performed through this insulating film.

  Plasma treatment and ozone treatment for the purpose of surface cleaning, surface activation, and the like are performed on the bonding surfaces of the single crystal Si substrate 10 and the transparent insulating substrate 20 on which the ion implantation layer 11 is formed in this manner (FIG. 1 (D)). Such a surface treatment is performed for the purpose of removing the organic substances on the surface to be the bonding surface or increasing the OH group on the surface so as to activate the surface, and is transparent to the single crystal Si substrate 10. It is not always necessary to perform treatment on both bonding surfaces of the conductive substrate 20, and it may be performed only on one of the bonding surfaces.

  When performing this surface treatment by plasma treatment, a surface-clean single crystal Si substrate and / or a transparent insulating substrate that has been subjected to RCA cleaning or the like is placed on a sample stage in a vacuum chamber, and the inside of the vacuum chamber is The plasma gas is introduced to a predetermined degree of vacuum. Examples of the plasma gas used here include oxygen gas, hydrogen gas, argon gas, or a mixed gas thereof, or a mixed gas of hydrogen gas and helium gas, for surface treatment of a single crystal Si substrate. The surface condition and purpose of the single crystal Si substrate can be changed as appropriate.

  When the surface treatment is intended to oxidize the single crystal Si surface, a gas containing at least oxygen gas is used as the plasma gas. Note that when a transparent insulating substrate such as a quartz substrate whose surface is in an oxidized state is used, there is no particular restriction on the selection of such a plasma gas species. After the introduction of the plasma gas, high-frequency plasma with a power of about 100 W is generated, the surface of the single crystal Si substrate and / or the transparent insulating substrate to be plasma-treated is subjected to treatment for about 5 to 10 seconds, and the process is terminated.

  When the surface treatment is performed by ozone treatment, a surface-cleaned single crystal Si substrate and / or a transparent insulating substrate that has been subjected to RCA cleaning or the like is placed on a sample stage in an oxygen-containing chamber. A high-frequency plasma having a predetermined power after introducing a plasma gas such as nitrogen gas or argon gas into the chamber, oxygen in the atmosphere is converted into ozone by the plasma, and a single crystal Si substrate to be processed; The surface of the transparent insulating substrate is treated for a predetermined time.

  The single crystal Si substrate 10 and the surface of the transparent insulating substrate 20 that have been subjected to such a surface treatment are adhered to each other as a bonding surface (FIG. 1E). As described above, at least one surface (bonding surface) of the single crystal Si substrate 10 and the transparent insulating substrate 20 is activated by being subjected to surface treatment by plasma treatment, ozone treatment, or the like. Even in the (bonded) state, it is possible to obtain a bonding strength of a level that can sufficiently withstand mechanical peeling and mechanical polishing in the subsequent process. However, in the case where a higher bonding strength is provided, “ Subsequent to “bonding”, a sub-step of performing “bonding processing” by heating at a relatively low temperature may be provided.

  The bonding processing temperature at this time is appropriately selected according to the type of the substrate used for bonding, but the substrate bonded to the single crystal Si substrate is a quartz substrate, a sapphire (alumina) substrate, a borosilicate glass substrate, Alternatively, in the case of a transparent insulating substrate such as a crystallized glass substrate, the temperature is set to 350 ° C. or lower, for example, a temperature range of 100 to 350 ° C.

When the substrate to be bonded to the single crystal Si substrate is a transparent insulating substrate (particularly a quartz substrate), the temperature selection of 350 ° C. or lower is selected because of the difference in thermal expansion coefficient between the single crystal Si and quartz and the thermal expansion coefficient. The amount of strain due to the difference and the thickness of the single crystal Si substrate 10 and the transparent insulating substrate 20 are taken into consideration. If the thickness of the single-crystal Si substrate 10 and the transparent insulating substrate 20 is generally comparable thermal expansion coefficient of the thermal expansion coefficient of the single crystal Si and (2.33 × 10 ^-6) quartz (0.6 × 10 ^{- 6} ) Due to the large difference between them, when heat treatment is performed at a temperature exceeding 350 ° C., cracks due to thermal strain or peeling at the joint surface may occur due to the difference in rigidity between the two substrates. In an extreme case, the single crystal Si substrate or the quartz substrate may be broken. For this reason, the upper limit of the heat treatment temperature is selected to be 350 ° C., and the heat treatment is preferably performed in a temperature range of 100 to 300 ° C.

  Following such a bonding process, the back surface of the single crystal silicon substrate 10 of the bonded substrate is heated in close contact with a heating plate such as a hot plate (FIG. 1F).

  As described above, hydrogen ion implantation forms a “microbubble layer” localized in a region corresponding to the average ion implantation depth L, and this “microbubble layer” has a dangling bond. Si atoms and high-density “Si—H bonds” are generated, and the bonding state of elements in the “microbubble layer” and in the vicinity of the region is locally weakened. Therefore, the ion-implanted layer 11 in the state where the “microbubble layer” is formed is in a state where “opening” is likely to occur with a little heat energy.

  In addition, since silicon crystals have a larger coefficient of thermal expansion than transparent insulating substrate materials, even when heated at a relatively low temperature for a short time, a large stress is generated between the two substrates, and “open cleavage” tends to occur. The environment is obtained.

  In the present invention, the local chemical bond weakening in the ion implantation layer 11 of the single crystal Si substrate 10 into which hydrogen ions are implanted and the difference in thermal expansion coefficient between the Si substrate and the transparent insulating substrate 20 are utilized. Thus, the silicon thin film is peeled off by applying heat energy necessary for “opening” by short-time heating at a relatively low temperature.

  FIG. 2 is a conceptual diagram for explaining how the substrate is heated for peeling the silicon thin film. In this figure, reference numeral 30 denotes a heating unit. In this figure, a heating plate 32 having a smooth surface is placed on a hot plate 31, and the smooth surface of the heating plate 32 is bonded to the transparent insulating substrate 20. The single crystal Si substrate 10 is brought into close contact with the back surface. Although a dummy silicon substrate is used as the heating plate 32, there is no particular material limitation as long as a smooth surface can be easily obtained (semiconductor substrate or ceramic substrate). Silicone rubber or the like can also be used as a heating plate material, but since the heat-resistant temperature is considered to be about 250 ° C., it is not suitable for use at higher temperatures. In addition, if the surface of the hot plate 31 is sufficiently smooth, the hot plate 31 itself may be a “heating plate” without using the heating plate 32.

  The temperature of the heating plate 32 is maintained at a temperature of 200 ° C. or more and 350 ° C. or less. When the back surface of the single crystal Si substrate 10 bonded to the insulating substrate 20 is brought into close contact with the heating plate 32, the single crystal Si substrate 10 is thermally conductive. Is heated, and a temperature difference is generated between the transparent insulating substrate 20 and the transparent insulating substrate 20. As described above, since the thermal expansion coefficient of the silicon crystal is larger than the thermal expansion coefficient of the material used for the transparent insulating substrate, when the bonded single crystal Si substrate 10 is heated from the back surface, the single crystal Si substrate A large stress is generated between the two substrates due to the rapid expansion on the 10 side.

  In the case of heating using a normal diffusion furnace or the like, the single crystal Si substrate 10 and the transparent insulating substrate 20 in a bonded state are heated at the same time, and therefore stress caused by a difference in thermal expansion coefficient between the two substrates. Although the stress relaxation occurs before the silicon thin film is peeled off due to this stress, according to the heating method as described above, the abrupt single crystal Si is The expansion of the substrate 10 causes peeling at the hydrogen ion implantation interface.

  Here, the reason for setting the temperature of the heating plate 32 to 200 ° C. or more and 350 ° C. or less is that it is difficult to obtain the stress necessary for peeling the silicon thin film at a temperature lower than 200 ° C., which exceeds 350 ° C. This is because cracks are likely to occur at the bonding interface of the bonded substrate.

  In addition, before or after the peeling process of the silicon thin film by the heating plate 32, a sub-step for applying an external impact for promoting peeling from the end of the ion implantation layer 11 may be provided.

  FIG. 3 is a conceptual diagram for illustrating a technique for applying an external impact in the silicon thin film peeling step. Various methods for applying the impact are conceivable. For example, a fluid such as a gas or a liquid is jetted from the tip 41 of the nozzle 40 and sprayed from the side surface of the single crystal Si wafer 10. (FIG. 3A), or a method of applying an impact by pressing the tip portion 51 of the blade 50 against a region near the ion implantation layer (FIG. 3B).

  As described above, when the heat treatment as described above is performed, a chemical bond of Si atoms having an unpaired bond in the ion-implanted layer 11 or a break of the Si—H bond occurs, and as a result, the single crystal Si substrate 10 is cut. Separation of the silicon thin film 12 from the bulk portion 13 of single crystal silicon occurs along the crystal plane at a position corresponding to a predetermined depth (average ion implantation depth L) in the vicinity of the surface (FIG. 1G). The SOI layer 12 is obtained on the second substrate 20 (FIG. 1H).

  According to the experiments by the present inventors, the silicon thin film can be peeled off by heating the substrate at 300 ° C. for about 3 seconds. The surface of the SOI layer after peeling obtained in this way is in an extremely flat state without defects such as local peeling of the silicon thin film, peeling marks or untransferred areas. When an area of 10 μm × 10 μm on the surface of the SOI layer after peeling was measured with an atomic force microscope (AFM), the average value of RMS was as good as 6 nm or less.

  As described above, in the present invention, the high temperature treatment and the mechanical peeling treatment as in the conventional method are performed in any of the bonding step between the single crystal Si substrate 10 and the transparent insulating substrate 20 and the SOI layer peeling step. It is not necessary and can be processed at a low temperature (350 ° C. or lower) consistently. Many of the conventionally known methods for manufacturing SOI substrates include a high-temperature processing step, and therefore, special measures for avoiding cracks and peeling caused by thermal strain are necessary. Since the peeling process of the invention requires neither high-temperature treatment nor mechanical peeling treatment, an SOI substrate having an SOI layer excellent in film thickness uniformity, crystallinity, and various electrical characteristics (such as carrier mobility) is obtained. In addition to being able to be provided, it is extremely advantageous from the viewpoint of stabilization and simplification of the manufacturing process of the SOI substrate.

  According to the present invention, in the process of manufacturing an SOI substrate by laminating a single crystal silicon substrate and a transparent insulating substrate, cracks, local cracks, and the like due to differences in thermal characteristics between the substrates and mechanical damage are prevented. It is possible to avoid introduction into the SOI layer. As a result, it is possible to provide an SOI substrate having an SOI layer that is excellent in film thickness uniformity, crystallinity, and various electrical characteristics (such as carrier mobility).

It is a figure for demonstrating the example of a manufacturing process of the SOI substrate of this invention. It is a conceptual diagram for demonstrating the mode of the heat processing for a silicon thin film peeling. It is a conceptual diagram for the illustration of the method of giving an external impact in the peeling process of a silicon thin film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Single crystal Si substrate 11 Ion implantation layer 12 SOI layer 13 Bulk part 20 Transparent insulating substrate 30 Heating part 31 Hot plate 32 Heating plate 40 Nozzle 41 Nozzle tip 50 Blade 51 Blade tip

Claims (5)

A method for manufacturing an SOI substrate by consistently performing only a low temperature treatment of 350 ° C. or lower ,
A first step of forming a hydrogen ion implanted layer on the surface side of the first substrate which is a single crystal silicon substrate;
A second step of performing a surface activation treatment on at least one of the surface of the second substrate which is a transparent insulating substrate and the surface of the first substrate;
A third heat treatment is performed at a temperature of 100 to 300 ° C. in a state where the surface of the first substrate and the surface of the second substrate are in close contact with each other to bond the first substrate and the second substrate together. Step The back surface of the first substrate of the bonded substrates is brought into close contact with a heating plate maintained at a temperature of 200 ° C. or higher and 350 ° C. or lower to heat the first substrate, and a silicon layer is formed from the first substrate. And a fourth step of peeling and forming an SOI layer on the surface of the second substrate ,
The second substrate is either a quartz substrate, a sapphire (alumina) substrate, a borosilicate glass substrate, or a crystallized glass substrate.
A method for manufacturing an SOI substrate, comprising: ^{2. The} method for manufacturing an SOI substrate according to claim 1 , wherein an implantation amount (dose amount) of hydrogen ions in the first step is 1 × 10 ^{16 to} 5 × 10 ¹⁷ atoms / cm ² . 3. The method for manufacturing an SOI substrate according to claim 1, wherein the surface activation process of the second step is performed by at least one of a plasma process and an ozone process. 4. 4. The method for manufacturing an SOI substrate according to claim 1, wherein the heating plate used in the fourth step is a semiconductor substrate or a ceramic substrate having a smooth surface. 5. The fourth step, claims before or after heating of the first substrate, characterized in that it comprises a sub-step of applying an external impact for the separation promoting the end of the hydrogen ion implanted layer Item 5. The method for manufacturing an SOI substrate according to any one of Items 1 to 4 .

Images